Atomic form-factor measurements in the low-momentum transfer region for Li, Be, and Al by inelastic x-ray scattering

We report measurements of the atomic form factor of lithium, beryllium, and aluminum single crystals at low-momentum transfers (Q=1.6-50 nm(-1)) from the intensity of phonons observed by inelastic x-ray scattering. Comparing to Hartree-Fock calculations, the form factor deviates significantly in the case of lithium and beryllium around k(F). These deviations can be mostly understood on the basis of electron redistribution by a pseudopotential. The influence of multiple scattering due to coherent phonon scattering and possible deviations from the adiabatic approximation are also discussed.